PDF use a zero based numbering system for pages. The first page is page zero, 0, or the logical page -1.

You can go to any page with JavaScirpt using the 'pageNum' property which is an integer and you can read or write this data. Writing or setting the value of this properyt will navigate one to that page number.

Since the pageNum is an integer, you can increment it or decrement it to move to the next or previous page. You can use the numPages property to navigate to the last page.